OK, So to bring my long winded post to conclusion I ordered and received the correct stock Stihl parts to fit my MS 400:
Large clutch cover 1138-648-0400 $64.33
Brake cover 1140-021-1100 $7.68
Inner Spike 1135-664-0501
Outer spike 1135-664-0500
Spikes were $20.33 ea.
As stated earlier, I have done mechanical work on my own tractors, farm equipment, trucks, cars and many other items. Never has it been this difficult and time consuming. I am left with the impression that our dealers simply do not know how to cross reference parts between saws or just are unwilling to call Stihl and obtain the information.
Glad it’s behind me and thanks again to everyone‘s patience and kindness